Hybrids. Mules/Hinnys can come in any size or mixture of Horse/Donkey breeds.
Where the Sire is a Donkey and the Dam is a Horse mare the resulting progeny is a Mule. The reverse cross, where the Sire is a Horse Stallion and the Dam is a Donkey Jenny is called a Hinny.
Mules/Hinnys can often be bigger then their parents due to hybrid vigour.